1. Field of the Invention
The present invention relates to a partial plating system, more particularly relates to a technique useful for partial plating of a TAB tape and a lead frame.
2. Description of the Related Art
In recent years, along with the increasing compactness demanded for electronic apparatuses, the semiconductor packages for mounting in the electronic apparatuses have been made smaller in size. One type of such compacter semiconductor package is the tape carrier package (TCP). A TCP consists of a polyimide film or other support on which copper foil leads are formed. The copper foil leads and the terminals of the semiconductor devices are bonded together, then the entire assembly is sealed by a resin.
FIG. 13A is a plan view of part of a polyimide film on which such copper foil leads are formed. As shown in FIG. 13A, a plurality of copper foil leads 102, 102 . . . are formed on the polyimide film 101. Below, the polyimide film 101 on which the plurality of copper foil leads 102, 102 . . . are formed will be referred to as a tape automated bonding (TAB) tape 106. FIG. 133 is an enlarged view of such a copper foil lead. As shown here, the copper foil lead 102 is comprised of an inner lead 102a, an outer lead 102b, a test pad 102c, and parts connecting the same.
Among these, the inner lead 102a projects out toward the inside of a device hole 104 formed in the polyimide film 101. On the other hand, the outer lead 102b is formed at a position corresponding to a window hole 105 formed in the polyimide film 101.
The TAB tape 106 formed in this way is connected with an LSI or other semiconductor device (not shown) by inner lead bonding. In this inner lead bonding, the bumps (not shown) of the semiconductor device and the inner leads 102a are hot pressed together for electrical connection of the bumps and inner leads 102a. After mounting the semiconductor device in this way, the semiconductor device and the polyimide film 101 at the portion inside from the window holes 105 are sealed by a resin.
When the bumps of the semiconductor device are made of gold, however, it is preferable that the portions of the inner leads 102a to be hot pressed with the gold bumps be gold plated. This is because if they are gold plated, the gold plating and the gold contained in the gold bumps fuse with each other and improve the reliability of connection of the inner leads 102a and the gold bumps. Therefore, the general practice has been to gold plate the copper foil leads 102 after forming the copper foil leads 102 on the polyimide film 101.
Next, an explanation will be given, with reference to FIG. 15, of a plating system of the related art used in such a plating process.
FIG. 15 is a perspective view of an entire plating system according to the related art. The plating system 107 of the related art is comprised of a sparger tank 108, a nozzle 109 provided inside the same, and an anodic plate 110. The TAB tape 106 is transported toward the transport direction shown by the arrow in the figure by driving of a roller (not shown) engaged with sprocket holes 103, 103 . . . (see FIG. 13A) formed in the polyimide film 101. The TAB tape 106 is transported in a state held with its surface in the vertical plane (called xe2x80x9cvertical transportxe2x80x9d hereinafter). Note that the sparger tank 108 is formed with slits 108a, 108a at the portion where the TAB tape 106 is fed in and the portion where it is fed out.
When a TAB tape 106 is transported to the plating system 107, a plating solution is sprayed from the nozzle 109 to fill the inside of the sparger tank 108 with the plating solution. If current is sent to the copper foil leads 102 and the anodic plate 110 in this state using the copper foil leads 102 of the TAB tape 106 as cathodes, the copper foil leads 102 will be gold plated.
As explained above, however, the portions which require the gold plating in the copper foil leads 102 are the inner leads 102a. The rest of the portions do not require gold plating. According to the plating system of the related art, however, all of the portions of the copper foil leads 102 to which current was supplied end up being gold plated. If portions other than those requiring it are gold plated in this way, the expensive gold is used wastefully and the problem arises of a higher cost of the plating process.
An object of the present invention is to provide a partial plating system able to gold plate only the inner leads of a TAB tape.
To achieve the above object, according to a first aspect of the present invention, there is provided a partial plating system provided with a mask having an opening formed to correspond to a plating region of a TAB tape and provided horizontally; an elevating means for lowering the TAB tape toward the mask; and a pressing means for pressing the TAB tape on to the mask; a plating solution being sprayed from below the opening toward the opening to plate the plating region.
According to a second aspect of the invention, there is provided a partial plating system of the first aspect of the invention wherein the mask is provided on its surface with guide pins for engagement with engagement holes of the TAB tape and is placed on a base member so as to be able to slide in a horizontal plane around a predetermined reference position.
According to a third aspect of the invention, there is provided a partial plating system of the second aspect of the invention wherein a biasing member is provided between the elevating means and the base member and wherein the elevating means is biased to move away from the base member.
According to a fourth aspect of the invention, there is provided a partial plating system of any one of the first to third aspects of the invention further provided with a feeding means for transporting the TAB tape in a longitudinal direction by exactly a predetermined length after the partial plating system plates a certain length of the TAB tape in one plating operation.
According to a fifth aspect of the invention, there is provided a partial plating system of any of the first to fourth aspects of the invention wherein the elevating means is provided with a guiding means for use when the TAB tape is being transported in the longitudinal direction.
Next, the mode of operation of the present invention will be explained.
According to the partial plating system of the present invention, provision is made of a mask having an opening formed corresponding to the plating region of the TAB tape and provided horizontally. The TAB tape is lowered by the elevating means toward the mask, then is pressed against the mask by the pressing means, so the tape is pressed against the mask in a state with its surface held in the horizontal plane.
In the state pressed against the mask in this way, the plating region of the TAB tape is exposed from the opening. If the plating solution is sprayed from below the opening toward the opening in this state, the exposed plating region will be plated. At this time, since the portions of the TAB tape other than the plating region are covered by the mask, those portions will not be plated. Therefore, by recycling, the gold or other precious metals in the plating solution will not be used wastefully and the cost of the plating process can be reduced.
Further, by placing the mask horizontally and holding the TAB tape in the horizontal plane, the TAB tape is plated to a uniform thickness. That is, if the TAB tape is held in the horizontal plane, the plating solution will not flow over the surface of the plating solution after being sprayed. The amount of the plating solution deposited will become uniform and the plating thickness will therefore become uniform.
Further, according to the partial plating system of another aspect of the invention, guide pins for engagement with engagement holes of the TAB tape are provided on the surface of the mask. In this case, the mask is placed on a base member so as to be able to slide in the horizontal plane around a predetermined reference position. According to this, by engagement of the guide pins with the engagement holes of the TAB tape, the opening of the mask and the plating region of the TAB tape will be aligned in position and plating of portions other than the plating regions can be prevented.
Further, by placing the mask so as to be able to slide in the horizontal plane, it is possible to reduce the magnitude of the force acting on the TAB tape when the guide pins enter the engagement holes of the TAB tape. Therefore, even if the length of the TAB tape being transported to the partial plating system is made somewhat longer than when the mask cannot slide, the magnitude of the force acting on the TAB tape will never become larger than the case where the mask cannot slide. Due to this, it is possible to increase the length of the TAB tape plated in a single plating operation compared with when the mask cannot slide.
The partial plating system of the present invention is also applicable to partial plating of a lead frame, in which the lead frame is aligned with a mask by engaging the guide pins with engagement holes of the lead frame so that only a selected portion such as a die pad or a head of inner lead is subjected to plating.